Fish May Not Have Evolved Gills to Breathe

Peter Rombough, a biologist at Brandon University in Canada, has conducted a study on the functions of fish gills. He concludes that although gills may allow a fish to breathe, that might not be the original reason why they evolved:

In order to keep from shriveling like your fingers in the bathtub, fish must constantly exchange ions, such as sodium and potassium, with the water. Larval fish can exchange ions through their skin, and early fish likely used rudimentary gill structures known as branchial baskets. But when the salinity of the water changes rapidly--as happened when fish invaded freshwater habitats--fish would have needed a much more efficient way of exchanging ions with their environment. That means large, complex gills.

Link via reddit | Photo: US Department of the Interior

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lol, i wanted to point out that wording too. 'Evolution' descibes random mutation + propagation due to the new feature aiding survival and breeding. Since the mutation is random in the first place, nothing can evolve 'for a reason'. (but there can be 'a reason' why the evolution stuck around.)
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@dbsmall - You're right. This kind of wording creates so much unnecessary confusion about evolution - including the "wow" responses to sociobiology and evolutionary psychology. Most people I know - even smart ones - when asked to describe natural selection, end up describing something like Lamarkianism.
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I don't like the "reason for some evolutionary development" phrasing, even though I know what you mean.

There's the mutation---which has no *reason*, but which is the development in an individual or select set. and they were not developed *for a purpose*.

And then there's the selection---those mutants with superior traits for their circumstances survive and propagate that trait to their descendants.

So, gills weren't developed for ion exchange. Gills were *kept* in fish, because they facilitated ion exchange.

And suddenly, I'm even more impressed by Cristophe. He managed to be funny *and* avoid being a sycophant.
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